摘要
Surface structures of Pt-Sn and Pt-Fe bimetallic catalysts have been investigated by means of Mssbauer spectroscopy, Pt-L<sub>Ⅲ</sub>-edge EXAFS and H<sub>2</sub>-adsorption. The results showed that the second component, such as Sn or Fe, remained in the oxidative state and dispersed on the γ-Al<sub>2</sub>O<sub>3</sub> surface after reduction, while Pt was completely reduced to the metallic state and dispersed on either the metal oxide surface or the γ-Al<sub>2</sub>O<sub>3</sub> surface. By correlating the distribution of Pt species on different surfaces with the reaction and adsorption performances, it is proposed that two kinds of active Pt species existed on the surfaces of both catalysts, named M<sub>1</sub> sites and M<sub>2</sub> sites. M<sub>1</sub> sites are the sites in which Pt directly anchored on the γ-Al<sub>2</sub>O<sub>3</sub> surface, while M<sub>2</sub> sites are those in which Pt anchored on the metal oxide surface. M<sub>1</sub> sites are favorable for low temperature H<sub>2</sub> adsorption, and responsible for the hydrogenolysis reaction and carbon deposition, while M<sub>2</sub> sites which adsorb more H<sub>2</sub> at higher
Surface structures of Pt-Sn and Pt-Fe bimetallic catalysts have been investigated by means of M?ssbauer spectroscopy, Pt-L111-edge EXAFS and Hz-adsorption. The results showed that the second component, such as Sn or Fe, remained in the oxidative state and dispersed on the γ-Al2O3 surface after reduction, while Pt was completely reduced to the metallic state and dispersed on either the metal oxide surface or the γ-A1203, surface. By correlating the distribution of Pt species on different surfaces with the reaction and adsorption performances, it is proposed that two kinds of active Pt species existed on the surfaces of both catalysts, namedM1 sites and M2 sites. M1 sites are the sites in which Pt directly anchored on the γ-Al2O3 surface, while M2 sites are those in which Pt anchored on the metal oxide surface. MI sites are favorable for low temperature H2 adsorption, and responsible for the hydrogenolysis reaction and carbon deposition, while M2 sites which adsorb more H2 at higher temperature, are more resistant to the deactivation due to less carbon deposition, and provide major contribution to the dehydrogenation reaction.
